Electrostatically chargeable printing form



Sept 23, 1969 G. RnzERFELD 3,468,254

ELECTROSTATICALLY CHRGEABLE PRINTNG FORM Filed May 2l, 1965 2Sheets-Sheet 1 Fig.1

Inventor: 6 Qfdrd Eluibed Sept. 23, 1969 G, RITZERFELD ELEcTRosTATIcALLYCHARGEABLE PRINTING FORM Filed May 21, 1965 2 Sheets-Sheet Fig.3

Inventor:

United States Patent() 3,468,254 ELECTROSTATICALLY CHARGEABLE PRINTINGFORM Gerhard Ritzerfeld, Franzensbader Strasse 21, Berlin-Grunewald,Germany Filed May 21, 1965, Ser. No. 457,672 Claims priority,application 9Germany, May 28, 1964,

U.S. Cl. lOl-401.1 4 Claims ABSTRACT OF THE DISCLOSURE Anelectrostatically chargeable printing form is produced by contacting anelectrically conductive surface layer of a printing form blank with asurface layer of dielectric material having a melting point aboveambient temperature, preferably in the vicinity of 80 C., and applyingheat to selected portions of the layer of dielectric material,preferably by infrared radiation, so as to sufliciently heat thecontacting surface of the selected portions of the layer of dielectricmaterial to make the same actively adhesive and thereby to adhere theselected portions of the dielectric layer to the contacting electricallyconductive surface layer, thereby forming a printing form having anoperative surface consisting of the electrically conductive surfacelayer with the selected portions of dielectric material adheringthereto.

The present invention relates to a method and arrangement for producingelectrostatically chargeable printing forms from which copies of anoriginal may be produced. More particularly, the present invention isconcerned with printing forms which are produced from originals whichcontain heat or infrared ray absorbing image portions and substantiallyheat or infrared rays permeable image-free portions, for instance,originals which are formed by typing or printing on transparent paper.

It is an object of the present invention to provide a method forproducing electrostatically chargeable printing forms which can becarried out in a simple and economical manner.

It is a further object of the present invention to provide a method ofproducing electrostatically chargeable printing forms, whereby thedifference between the heat or infrared ray absorption characteristicsof image-forming and image-free portions of an original is utilized fortransferring selected portions of `dielectric material, corresponding tothe image to be reproduced, onto a printing form master.

It is yet a further object of the present invention to provide acomposite sheet arrangement which, when eX- posed to heat radiation,will result in the formation of an electrostatically chargeable printingform.

Other objects and advantages of the present invention will becomeapparent from a further reading of the description and of the appendedclaims.

With the above and other objects in View, the present inventioncontemplates a method of producing an electrostatically chargeableprinting form, comprising the steps of contacting an electricallyconductive surface layer of a printing form blank with `a surface of alayer of low melting dielectric material, and applying heat to selectedportions of the layer of dielectric material and to adhere the selectedportions to the electrically conductive surface layer, thereby forming aprinting form having `an operative surface consisting of theelectrically conductive surface layer with the selected portions ofdielectric material adhering thereto.

Patented Sept. 23, 1969 In accordance with a prefered embodiment, themethod of producing electrostatically chargeable printing forms, inaccordance with the present invention, comprises the steps of forming astack consisting essentially of a printing form blank composed of acarrier sheet and an electrically conductive layer consistingessentially of a metal selected from the group consisting of aluminum,cadmium, zinc and silver located on one face of the carrier sheet, anoriginal including image-forming, infrared-absorbing portions andimage-free substantially infraredpermeable portions, and interposedbetween the original and said printing form blank a transfer sheetcomposed of a substantially infrared-permeable carrier sheet and anelectrostatically chargeable layer of low melting point consistingessentially of a mixture of at least one hard wax and at least oneeasily electrostatically chargeable soft Wax and having distributedtherethrough at least one pulverulent dielectric material having amelting point higher than the melting point of the mixture, theelectrostatically chargeable layer being located on one face of thecarrier sheet, the carrier sheet of the transfer sheet contacting theoriginal and the electrostatically chargeable layer of the transfersheet contacting the electrically conductive layer of the printing formblank, subjecting the thus formed stack to infrared radiation in thedirection from the original towards the printing form blank so as toheat the infrared-absorbing image-forming portions of the original andcorresponding portions of the electrostatically chargeable layer therebymelting the corresponding portions at least in contact with theelectrically conductive layer and causing adherence of the correspondingportions of the electrostatically chargeable layer to the electricallyconductive layer, allowing the corresponding portions of theelectrostatically chargeable layer to cool below the melting pointthereof, and separating the printing form blank with the correspondingportions of the electrostatically chargeable layer from the stack, thusforming a printing form having an operating face consisting of theelectrically conductive layer with the selected electrostaticallychargeable portions thereon.

It is also within the scope of the present invention to provide .acomposite sheet arrangement adapted for forming an electrostaticallychargeable printing form, comprising, in combination, a first sheetmember consisting essentially of a non-conductive carrier sheet and anelectrically conductive surface layer on one face thereof, a secondsheet member consisting essentially of a substantially infraredradiation-permeable carrier sheet and a low melting layer of dielectricmaterial on one face thereof, the low melting layer of dielectricmaterial of the second sheet member contacting the electricallyconductive surface layer of the first sheet member, and an imagecarrying sheet including image-forming, infrared-absorbing portions andimage-free substantially infrared-permeable portions, contacting thecarrier sheet of the second sheet member, whereby upon exposure of theimage carrying sheet to infrared radiation the image-forming,infrared-absorbing portions and corresponding portions of the lowmelting layer of dielectric material will be heated so as to makecorresponding portions of the layer of dielectric material in contactwith the electrically conductive surface layer actively adhesive,thereby adhering the corresponding portions of the dielectric layer tothe electrically conductive surface layer, thereby forming anelectrostatically chargeable printing form consisting essentially of thenon-conductive carrier sheet with the electrically conductive surfacelayer on one yface thereof and the selected portions of the layer ofdielectric material adhering to the electrically conductive surfacelayer.

Thus, according to the present invention, the conductive surface of aprinting form blank is contacted with a dielectric and electrostaticallychargeable layer of .a transfer sheet, whereby the dielectric layer isformed of an easily electrostatically chareable material of relativelylow melting point. Transfer of portions of the dielectric layer from thetransfer sheet to the printing form blank, in accordance with theimage-forming portion of an original, is then `accomplished byselectively heating the imageforming portion of the dielectric transferlayer, for instance by means of infrared radiation which first contactsthe original which is to be reproduced by means of th printing form.

Preferably, the dielectric, easily electrostatically chargeable layer ofthe transfer sheet will be formed of a mixture of hard wax such asmontan wax and/or candelilla wax on the one hand, and anelectrostatically easily chargeable soft wax such as beeswax. Y

According to a preferred embodiment of the present invention, apulverulent dielectric material which has a melting point higher thanthe melting point of the wax mixture is distributed through and embeddedin the dielectric layer. Suitable pulverulent dielectric materials are,for instance, synthetic plastic materials such as cellulose-triesters,for instance cellulose-triacetate, and nitrocellulose, orpolycarbonates, or polyesters, known to those skilled in the art,whereby, however, such pulverulent dielectric materials should be chosenwhich, as mentioned above, have a melting point higher than the meltingpoint of the wax mixture.

The printing form blank to which selected portions of the dielectrictransfer layer are to be adhered, preferably will consist -of a foil ofsynthetic material, for instance an acetate foil, having a thin metallayer, for instance an aluminum, silver, cadmium or zinc layer appliedto one face thereof, for instance by vapor deposition.

The carrier sheet of the transfer sheet, which carries the easilymeltable layer of dielectric material also will consist preferably of afoil of synthetic material, for instance a polyester or polycarbonatefoil such as are per se well known in the art. It is also possible toreplace the carrier sheets of synthetic material with` suitably thin,heat rays, particularly infrared rays-permeable, paper.

The transfer of the image from an original onto a printing form blank,in the form of selected portions of an electrostatically chargeable,dielectric transfer layer may be carried out, according to the presentinvention, in the following manner:

The image is formed on a support which is permeable to a high degree forheat rays, particularly infrared rays. The image itself, for instanceprinted or typed indicia, are formed of a material which stronglyabsorbs heat rays, particularly infrered rays. The transferable,dielectric layer of the transfer sheet preferably will have a lowabsorptivity for heat rays, so that the heat radiation contacts rst thecarrier sheet of the image, preferably at the side thereof which isopposite to the face on which the image-forming indicia or the like arelocated, and the heat is then transferred from the heat absorbingindicia or the like to the carrier sheet of the transfer sheet and fromthere, passing through the dielectric transferable layer, to theconductive layer ofthe printing form blank.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with .additional objects and advantages thereof,will be best understood from the following description of specieembodiments when read in connection with the accompanying drawings, inwhich:

FIG. 1 is a schematic, elevational, cross sectional, exploded view of acomposite sheet arrangement according to the present invention;

FIG. 2 is a schematic, cross sectional, elevational view of the sheetarrangement while the same is exposed to infrared radiation; and

FIG. 3 is a schematic, elevational, cross sectional View of the sheetsof the sheet arrangement of FIG. 2, after completion of radiation of thesame with infrared rays and separation of the individual sheet members.

Referring now to the drawing, and particularly to FIG. 1, the printingform blank is shown consisting of a carrier sheet 1 of paper or of asynthetic foil, and an electrically conductive layer 2 adhering to oneface of carrier sheet 1 and consisting of a metal such as aluminum,silver, cadmium or zinc. The conductive layer 2 is preferably formed byvapor deposition in a thickness of about 1 micron. Foil 1 may consistfor instance of a cellulosetriester, polyvinyl chloride, polyvinylacetate, polyethylene, polyethyleneterephthalate or polystyrene.

The transfer sheet consists of a carrier sheet 3 which should be highlypermeable for infrared rays and which may be formed of paper or a foilof synthetic material. Preferably so-called condenser paper, having athickness of only about 15 microns, or a foil ofpolyethyleneterephthalate, also having a thickness of about 15 micronsis used as carrier sheet 3.

A layer 4 which melts at a relatively low temperature, preferably atabout C. is located on one face of carrier sheet 3. Layer 4 preferablywill consist of a mixture of electrostatically chargeable hard and softwaxes. Certain hard waxes such as montan or candelilla wax possess thedesired electrostatic chargeability, however, a layer which consistsexclusively of hard waxes generally is too brittle and, in view thereof,preferably a mixture of hard and soft waxes is used for forming layer 4.

It has been found that many of the saft waxes, fats and oils which couldbe mixed with hard Wax in order to reduce the brittleness thereof, arenot suitable for the intended purpose, because these plasticizers areincapable of retaining electric charges or only capable of retainingelectric charges to a very slight degree. Thus, the electricchargeability of the hard waxes could be reduced by admixture of suchunsuitable plasticizers to such an extent that the thus formed mixturewould no longer be capable to serve for producing electrostaticallychargeable printing forms. However, there exist several plasticizers,particularly soft waxes which are capable of retaining electric chargesto a suicient degree. These soft waxes include for instance beeswax.Furthermore, a mixture of beeswax and electrostatically chargeablepulverulent materials of small particle size such as polyesters orpolycarbonates may be combined with hard wax.

The hard waxes which are suitable for forming one component of atransfer layer 4 include, in addition to montan wax and candelilla wax,also chlorinated waxes, for instance those which are obtainable underthe trade name Nibren Wax, and synthetic waxes, for instance varioustypes of synthetic waxes which are commercially available from theBadischen Anilinund Soda-Fabriken, and which are marketed under thedesignations:

Melting point, C.

OP-wax about O-wax about 100 A-wax 10S-105 SPO-wax 92-98 E-wax 79-82ES-wax 79-8Z S-wax 80-83 L-wax 80-8 3 V-wax 48-5 0 wax mixturepreferably will be equal to between and 30% of the weight of the waxmixture.

Suitable pulverulent materials include polyvinyl chloride, polystyreneand polyethylene.

The following examples of suitable compositions of layer 4 are given asillustrative only without, however, limiting the invention to thespecific details of the examples.

Example I Percent Montan wax 80 Ozocerite Example II Percent Montan wax7() Ozocerite 27 Aerosil 3 Example III Percent Montan Wax 80Benzophenone 17 Aerosil 3 Example IV Percent Montan wax 60 Spermaceti 37Aerosil 3 Example V Percent Montan wax `60 Spermaceti 30 Polyvinylchloride 10 Example VI Percent Montan Wax 60 Beeswax 40 Example VIIPercent Candelilla wax 60 Ozocerite 40 Example VIII Percent Candelillawax 60 Spermaceti 40 Furthermore, FIG. 1 illustrates a schematic crosssection through an original consisting of carrier sheet 5, for instancea paper sheet, an image-forming element 6 which includes an infraredrays-absorbing material, such as a dye, for instance an earthy ormineral pigment dye or printing and typewriter inks or a heavy metalsalt. A specific infrared absorbing material is: smoke or lamp black.

FIG. 2 illustrates a stack -formed of printing form blank 1, 2, transfersheet 3, 4, and original 5, 6.

The image-forming portions 6 of the original are heated by infrared raysemanating from radiator 7. The rays penetrate through infrared-permeablecarrier sheet 5 of the original so that a thermal image is formedcorresponding to the image-forming portions 6 of the original, and thethermal energy thereof is carried by convection through carrier sheet 3of transfer sheet 3, 4 to the transferable layer 4 of the transfersheet. The thermal energy corresponding to image-forming portions 6suffices to melt the corresponding portions of layer 4. This will causethe molten portions of layer 4, which in FIG. 3 are indicated byreference numeral 4b, to adhere to electrically conductive layer 2 ofprinting form blank 1, 2.

Upon allowing the stack to cool below the melting point of layer 4, andseparating of the sheet members of the stack into printing form,transfer sheet and original, it will be found that the initially moltenportions of transfer layer 4 will separate from carrier sheet 3 of thetransfer layer and will adhere to electrically conductive layer 2 of theprinting form blank, thereby converting the printing form blank into aprinting form.

Portions 4a of transfer layer 4 which correspond to the image-freeportions of original 5, 6 and which have not been exposed to such heat,will be retained on carrier sheet 3 of the transfer sheet and will formthereon a negative of image 6.

The image-forming portions 4b which now adhere to the electricallyconductive layer 2 of the printing form are electrostaticallychargeable.

In order to keep the heat requirement of this thermographic copyingprocess as small as possible, it is desirable to keep layer 4 as thin aspossible. On the other hand, the potential of the electric charge of adielectric layer having a thickness of less than l0 microns dropsconsiderably and, consequently, the most desirable thickness of layer 4is about l0 microns.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt is for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of the invention and,therefore, such adaptations should and are intended to be comprehendedwithin the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. A method of producing an electrostatically chargeable printing form,comprising the steps of forming a stack consisting essentially of aprinting form blank composed of a carrier sheet and an electricallyconductive layer located on one face of said carrier sheet, an originalincluding image-forming, infrared-absorbing portions and image-freesubstantially infrared-permeable portions, and interposed between saidoriginal and said printing form blank a transfer sheet composed of asubstantially infrared-permeable carrier sheet and an electrostaticallychargeable layer having a melting point above ambient temperatureconsisting essentially of a mixture of at least one hard wax and atleast one easily electrostatically chargeable soft wax and havingdistributed therethrough between 10 and 30% of the weight of saidmixture of at least one pulverulent dielectric material having aparticle size of up to 30l microns and having a melting point higherthan the melting point of said mixture, said electrostaticallychargeable layer being located on one face of said carrier sheet, saidcarrier sheet of said transfer sheet contacting said original and saidelectrostatically charegable layer of said transfer sheet contactingsaid electrically conductive layer of said printing form blank;subjecting the thus formed stack to infrared radiation in the directionfrom said original towards said printing form blank so as to heat saidinfraredabsorbing image-forming portions of said original andcorresponding portions of said electrostatically charageable layer to atleast the melting point of the latter thereby melting said correspondingportions at least in contact with said electrically conductive layer andcausing adherence of said corresponding portions of saidelectrostatically charageable layer to said electrically conductivelayer; allowing said corresponding portions of said electrostaticallychargeable layer to cool below the melting point thereof; and separatingsaid printing form blank with said corresponding portions of saidelectrostatically chargeable layer from said stack, thus forming aprinting form having an operating face consisting of said electricallyconductive layer with said selected electrostatically chargeableportions thereon.

2. A method as defined in claim 1, wherein the melting point of saidelectrostatically chargeable layer of said transfer sheet is in thevicinity of about C.

3. A composite sheet arrangement adapted for use in forming anelectrostatically chargeable printing form, comprising, in combination,a first sheet member consisting essentially of a non-conductive carriersheet and an electrically conductive surface layer consistingessentially of a metal selected from the group consisting of aluminum,cadmium, zinc and silver on one face thereof; a second sheet memberconsisting essentially of a substantially infrared radiation-permeablecarrier sheet and a layer of dielectric material having a melting pointabove ambient temperature on one face thereof, said layer 4of dielectricmaterial of said second sheet member contacting said electricallyconductive surface layer of said rst sheet member and consistingessentially Of a mixture of between about 60 and 80% by weight of atleast one hard wax and between about 40 and 20% by weight of at leastone easily electrostatically chargeable soft wax and having distributedtherethrough in an amount equal to between about 10 and 30% of theweight of said mixture at least one pulverulent dielectric material hav-UNITED STATES PATENTS 2,297,691 10/1942 Carlson lOl-149.4 XR 2,357,80912/1944 CarlSOn. 3,120,611 2/1964 Lind. 3,122,997 3/1964 Raczynski etal. lOl-149.2

EDGAR S. BURR, Primary Examiner U.S. Cl. X.R.

lOl-426; 1l7-36.l

